We propose to use high pressure liquid chromatography to study the influx of ascorbic acid into intestinal mucosal cells and to determine specifically whether the cell metabolizes ascorbic acid to dehydroascorbic acid. In addition, we hope to determine whether ascorbic acid is transported across the basolateral membrane into blood as ascorbic acid or as its metabolite, dehydroascorbic acid. The same techniques will be used to measure the amount of ascorbic acid and dehydroascorbic acid in various organs of animals on a normal diet, ascorbic acid-free diet, and high ascorbic acid diet. Our present data indicate that absorption of pyridoxine is linear when low concentrations of this vitamin are present on the mucosal surface. More detailed influx studies will be done to determine whether saturation kinetics apply and whether active transport takes place. The same types of studies will be done with riboflavin. The possible sodium-dependence of both these substances will be evaluated by influx studies done with the vitamin present in a sodium-containing and in a sodium-free solution on the mucosal surface.